(1) Field of the Invention
This invention relates to spectrometers adapted for the analysis of surfaces in which ions indicative of the surface composition are detected. In particular, such spectrometers preferably infer the composition of the surface from a determination of the decrease in a kinetic parameter such as energy associated with ions scattered off the surface.
(2) Description of the Prior Art
Various techniques and apparatus for analyzing surfaces by scattering ions from the surfaces are disclosed in U.S. Pat. Nos. 3,480,774, issued to Smith on Nov. 25, 1969, 3,665,182 issued to Goff and Smith on May 23, 1972 and 3,665,185, issued to Goff on May 23, 1972. Such techniques include impinging a primary ion beam on a sample. The energy of the ions scattered at a given angle is thereafter measured and the intensity of a signal associated with the measured scattered ions is plotted as a function of the ratio of energy of the scattered ions to that of the impinging ions (i.e., E.sub.1 /E.sub.o) to at least semiquantitatively identify the elemental composition of the bombarded surface. In the techniques disclosed in these patents, signals resulting from the passage of sputtered ions through the energy analyzer have generally been observed and measured, even when neutralization of surface charge buildup is achieved. The presence of the signal generally attributed to sputtered ions decreases the overall signal-to-noise ratio, and obscures the detection of scattered ions having a low ratio of E.sub.1 /E.sub.o, which low ratios correspond to those ions that have lost a large fraction of their incident energy as a result of being scattered from surface elements of relatively low atomic mass.